1. Field of the Invention
This invention concerns a protective flap in one or several layers, the uppermost layer being of wadding, which flap covers the releasable seam in needle-felts to be used in machines, as press felts, drying felts, conveyor belts or felts.
2. Description of the Prior Art
Endless felts are used in paper machines in order to convey and support the wet and weak web through the presses and the press section. Felts are also used in the drying section--specifically in marking sensitive positions--in order to convey the web through the drying section, whereby the web is pressed by the felt against heated cylinders. One of the most important requirements of the felts is that they do not give impressions on the wet web. Such felts have therefore earlier been furnished endless even if this has made it more difficult to mount them in the paper machine. Drying felts have for many years been provided with a seam in order to facilitate the mounting in the paper machine and during the last three years also the press felts have been provided with such a seam. In order to prevent that the paper web is marked by the seam, the seam is covered by a wadding flap, which is a continuation of the wadding layer which is fastened to the felt. The wadding flap is worn in different ways when the felt is used in the paper machine and its firmness will therefore decide the limit for the effective lifetime of the felt and marking in the web will occur due to the wearing of the wadding flap.
Felts which are provided with the above-mentioned seams are so called needle-felts which have a substrate on which a fibrous web, a layer of wadding is fastened. The layer of wadding is usually produced from carded fibrous web, which is placed transversely by an operating means with a breadth, which is in accordance with that of the substrate. The wadding layer is fastened to the substrate by several needles having downwardly directed hooks which penetrate the wadding layer and the substrate so that the fibers of the wadding layer are drawn downwardly between the yarns of the substrate and are fastened.
By this way of covering the substrate by wadding, the fibers of the wadding layer and of the so formed wadding flap over the seam are given a direction, which mainly is transverse to the longitudinal direction of the felts or the moving direction in the machines.
In the wadding flap where the fibers are not needled into the substrate but only penetrated so that the fibers are wound around and tied to each other, the strength in the operating direction will be very low. Fibers very often become loose by strains in the paper machine and the wadding flap can after a certain time fail to fulfil its function as a cover over the seam for preventing marking of the web.
The connection between the wadding flap, the paper machine and the web will be discussed hereinbelow.
A bad or worn out wadding flap in the press section will result in: a risk of marking, breakage of the web, disturbing of the operation of the press, disturbing of the vacuum system and the fiber passage. The elements in the press section which are wearing on the wadding flap are: suction boxes, HT-strips, press cylinders and guiding rollers. A wadding flap which is bad or worn out in the drying section will result in: risk of marking, breakage of the web and air leakage at so called ejector blowing boxes.
Matters which have influence on the strength of the wadding flap in the drying section are: wear of the cylinders and the guiding rollers, chemical degradation and hydrolysis and air blowing for cleaning.